Interference-seal plunger for an artificial lift system

ABSTRACT

A plunger for an artificial lift system and embodiment of the plunger includes a solid body adapted to travel within a production string positioned in a wellbore. At least one sealing ring connected about the body. The at least one sealing ring having an inner surface, an outer surface, a width and a thickness. The width is sufficient such that when the body is disposed in the production string the outer surface contacts and substantially forms a seal between the body and an inner wall of the production string. The at least one sealing ring having an outside diameter greater than the inner diameter of the production tubing within which the body is adapted to travel such that when the body is disposed within the production string an interference fit causes the sealing rings to roll-form into a constricted shape and diameter that exerts the sealing contact with the production string.

FIELD OF THE INVENTION

The present invention relates in general to producing fluids from a well and more specifically to an interference-seal plunger for a plunger lift system.

BACKGROUND

In the life of most wells the reservoir pressure decreases over time resulting in the failure of the well to produce fluids utilizing the formation pressure solely. As the formation pressure decreases, the well tends to fill up with liquids, such as oil and water, which inhibits the flow of gas into the wellbore and may prevent the production of liquids. It is common to remove this accumulation of liquid by artificial lift systems such as plunger lift, gas lift, pump lifting and surfactant lift wherein the liquid column is blown out of the well utilizing the reaction between surfactants and the liquid.

One method of producing fluids from a declining well having gas production is by utilizing a plunger lift system. A well is shut-in allowing a plunger to fall through the fluid column to the bottom of the well. When gas pressure from the formation is sufficient, the well may be opened allowing the gas to lift the plunger and the fluid above the plunger to the surface for production. The plunger acts as an interface between the gas and liquid in the well. However, when gas pressure is overcome by the hydrostatic head in the well, well production will cease.

Prior art plunger systems include spiral, brush, pad and cup plungers. The plungers may also be bypass plungers or solid or non-bypass plungers. Bypass plungers include a pathway formed through the plunger to facilitate the plunger's descent in the wellbore. A detachable plug is captured and seals the pathway for ascent in the wellbore. The plug is then dislodged at the top of the well allowing the plunger to again descend. Bypass plungers allow for a more efficient seal to be formed between the plunger and the production string. Bypass plungers allow fluid to bypass the plunger in its descent, thus, allowing liquid to accumulate on top of the plunger prior to its ascent.

Prior art solid or non-bypass plungers on the other hand typically sacrifice sealing efficiency between the production string and the plunger to facilitate operation. Prior art cup plungers, casing plungers, are utilized that include a stiff sealing element between the plunger and the casing to increase sealing efficiency. These casing plungers require sufficient weight to overcome the friction between the plunger and the production string and thus are limited to use in casing. Casing plungers also tend to get stuck requiring fishing operations.

It is thus a desire to provide a plunger that addresses the drawbacks of the prior art plungers. It is a still further desire to provide a plunger that provides efficient sealing between the plunger and the production string. It is a still further desire to provide an interference-seal between a plunger and the production string.

SUMMARY OF THE INVENTION

Accordingly, an embodiment of a plunger for an artificial lift system includes a solid body adapted to travel within a production string positioned in a wellbore and at least one sealing ring having an inner surface, an outer surface, a width and a thickness, the sealing ring connected about the body. When the body is positioned within the production string, the outer surface contacts and substantially forms a seal between the body and the production string.

The at least one sealing ring may include an inner portion proximate the inner surface formed of a substantially rigid material and an outer portion extending from the inner portion to the outer surface formed of a material substantially flexible relative to the inner portion. The at least one sealing ring may be connected about the body within a recess formed proximate a top end of the body. The at least one sealing ring may be connected about the body within a recess formed proximate a bottom end of the body. The plunger may include a plurality of plunger sealing rings.

The sealing rings may have an outside diameter greater than the inner diameter of the production tubing within which the body is adapted to travel such that when the body is disposed within the production string, an interference fit causes the sealing rings to roll-form into a constricted shape and diameter that exerts the sealing contact with the production string.

In another embodiment the plunger may include a solid body adapted to travel within a production string positioned in a wellbore. At least one sealing ring is connected about the body. The at least one sealing ring having an inner surface, an outer surface, a width and a thickness. The width is sufficient such that when the body is disposed in the production string, the outer surface contacts and substantially forms a seal between the body and an inner wall of the production string. The at least one sealing ring has a width to thickness ratio within a range from about 0.02 to 0.2 wherein when the body is disposed within the production string, the sealing ring assumes a shape such that the sealing ring enhances movement of the body over the drag from the sealing contact.

In another embodiment the plunger may include a solid body adapted to travel within a production string positioned in a wellbore. At least one sealing ring connected about the body. The at least one sealing ring having an inner surface, an outer surface, a width and a thickness. The width is sufficient such that when the body is disposed in the production string, the outer surface contacts and substantially forms a seal between the body and an inner wall of the production string. The at least one sealing ring having an outer diameter that is between about 3% to about 6% larger than an inner diameter of the production string within which it is adapted to travel.

The foregoing has outlined the features and technical advantages of the present invention in order that the detailed description of the invention that follows may be better understood. Additional features and advantages of the invention will be described hereinafter which form the subject of the claims of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

The foregoing and other features and aspects of the present invention will be best understood with reference to the following detailed description of a specific embodiment of the invention, when read in conjunction with the accompanying drawings, wherein:

FIG. 1 is a schematic drawing of an embodiment of a plunger lift system utilizing an interference-seal plunger of the present invention;

FIG. 2 is a side view of an embodiment of an interference-seal plunger of the present invention;

FIG. 3 is a partial cross-sectional view of an interference-seal plunger ascending in the production string; and

FIG. 4 is a partial cross-sectional view of an interference-seal plunger descending in the production string.

DETAILED DESCRIPTION

Refer now to the drawings wherein depicted elements are not necessarily shown to scale and wherein like or similar elements are designated by the same reference numeral through the several views.

As used herein, the terms “up” and “down”; “upper” and “lower”; and other like terms indicating relative positions to a given point or element are utilized to more clearly describe some elements of the embodiments of the invention. Commonly, these terms relate to a reference point as the surface from which drilling operations are initiated as being the top point and the total depth of the well being the lowest point.

FIG. 1 is a schematic drawing of an embodiment of a plunger lift system 5 utilizing an interference-seal plunger of the present invention, generally denoted by the numeral 10. The well includes a wellbore 12 extending from the surface 14 of the earth to a producing formation 16. Wellbore 12 may be lined with a casing 18 including perforations 20 proximate producing formation 16. The surface end of casing 18 is closed at surface 14 by a wellhead generally denoted by the numeral 24. A casing pressure transducer 26 is mounted at wellhead 24 for monitoring the pressure within casing 18.

A tubing string 22 (production string) supported by wellhead 24 is disposed within casing 18 and in fluid connection with a production “T” 28. Production “T” 28 includes a lubricator 30, also referred to as a catcher, a flow line 32 and a flow-control valve 34 connected to a controller 36. Production “T” 28 typically further includes a tubing pressure transducer 38 for monitoring the pressure in tubing 22. Positioned proximate the bottom of the well and in connection with production string 22 is a standing valve 44 and spring 46.

Wellbore 12 is filled with fluid from formation 16. The fluid includes liquid 40 and gas 42. As is well known in the art of lift systems, the fluid in the well includes liquid 40, gas 42, condensate and mixed phases. Plunger 10 is illustrated in the middle of a stroke and best described as descending in production string 22.

Interference-seal plunger 10 includes a plurality of sealing elements 48. Sealing elements 48 substantially form a seal between production string 22 and body 50 of plunger 10. A further description of plunger 10 is provided with reference to FIGS. 2-4.

FIG. 2 is a side view of an embodiment of an interference-seal plunger 10. Plunger 10 includes body 50 having a top end 52 having a fishing neck connection, middle section 58, a bottom end or shoe 60 and at least one sealing member 48. In the embodiment illustrated, body 50 is solid and does not include a bypass. It should further be understood that plunger 10 may include elements not illustrated such as, but not limited to, pads or brushes.

In the illustrated embodiment, plunger 10 includes two sets of sealing members 62 a, 62 b. Each set includes at least one sealing member 48 and may include a plurality of sealing members 48. First set 62 a of sealing members 48 is positioned proximate the top end 52 and separated from second set 62 b of sealing members 48 that are positioned proximate bottom end 60 by middle section 58.

Inner surface 64 is connected about outer surface 68 of body 50 such that it circumscribes body 50 and extends beyond the outside diameter of body 50. The outside diameter is defined as the largest diameter portion of plunger 50. Sealing members 48 may be connected about body 50 in a cavity 61 or along a reduced diameter section of body 50. It should be understood that sealing member 48 may be removably connected to body 50 to permit replacement or formed as part of a one-piece molded plunger 10.

Sealing members 48 are ring shaped members having an inner surface 64 and an outer surface 66. Sealing ring 48 is constructed substantially of a readily pliable elastomeric material. It should be understood that portions of sealing ring 48 may be formed of different materials or material having different physical characteristics. For example, the inner portion 47 (FIGS. 3 and 4) of sealing ring 48, proximate inner surface 64, may be formed of a substantially rigid material such as plastic or a metal to facilitate connection to the outer surface 68 of body 50 and to provide form and shape. The outer portion 49 (FIGS. 3 and 4) of sealing ring 48 may be formed of a more pliable and/or flexible material than inner portion 47. Description of features and characteristics of outer portion 49 are described at times herein with reference generally to sealing ring 48.

Sealing ring 48 (outer portion 49) is flexible in that its shape can be distorted then returned to it natural shape without substantial damage. Outer surface 66 is adapted for sealing contact with the internal wall 70 of production string 22 (shown in FIGS. 3 and 4). Sealing ring 48, portion 49, has the ability to readily abandon its natural shape and bend in the presence of a limited applied force. Ring 48 is desirably thin for flexibility and to counteract the effects of gas entrainment. In an embodiment of the invention sealing ring 48 has a width 72 to thickness 74 ratio within a range of from about 0.02 to about 0.20.

Reference is now made to FIGS. 3 and 4, wherein FIG. 3 is a partial cross-sectional view of plunger 10 ascending in production string 22 and FIG. 4 is a partial cross-sectional view of plunger 10 descending in production string 22. In use, sealing rings 48 form a barrier membrane separating the fluid above plunger 10 from the fluid below plunger 10. The outer ring diameter (outer surface 66) of sealing ring 48 is from about 3% to about 6%, desirably 5%, larger than the inner diameter (inner wall 70) of production string 22. This dimension produces an interference fit between sealing ring 48 and inner production string wall 70. The interference fit causes the outer portion 49 of sealing ring 48 to roll-form into a constricted shape and diameter that exerts a sealing contact 76 with the inner production tubing wall 70.

A desired shape of sealing ring 48 is planer in construction with a width to thickness ratio that allows sealing ring 48 to form in use to an optimized shape. The shape assumed by sealing ring 48 balances the pressure differential across plunger 10 with the drag created by the seal contact area 76. The shape assumed by sealing ring 48 balances the pressure differential by allowing and urging plunger 10 to move in the direction that reduces the pressure differential. The size and interference fit of the seal produces a shape of sealing ring 48 that enhances lift over drag. Wherein “lift” describes movement either ascending or descending in production string 22.

FIG. 3 illustrates the shape of sealing ring 48 (outer portion 49) during the upward travel of plunger 10. The domed shaped is caused by a pressure differential typically of approximately three psi. FIG. 4 illustrates the shape of plunger 10 as it descends in production string. The oversizing of sealing ring 48 causes sealing ring 48 to partially curl. The pressure is substantially equalized above and below sealing ring 48 and the friction (drag) at seal contact 76 causes sealing ring 48 to curl.

The number of sealing rings 48 is a variable dependent on the well applications. Some wells have varying diameter sections. Thus, varying sealing ring 48 dimensions may be utilized. The width to thickness ratio of sealing ring 48 needs to be sufficient to withstand the pressure differential and maintain sealing contact 76 and thin enough to permit sealing ring 48 to change shape and roll into a new shape during reciprocation of travel of plunger 10.

From the foregoing detailed description of specific embodiments of the invention, it should be apparent that an interference-seal plunger for an artificial lift system that is novel and unobvious has been disclosed. Although specific embodiments of the invention have been disclosed herein in some detail, this has been done solely for the purposes of describing various features and aspects of the invention and is not intended to be limiting with respect to the scope of the invention. It is contemplated that various substitutions, alterations, and/or modifications, including but not limited to those implementation variations which may have been suggested herein, may be made to the disclosed embodiments without departing from the spirit and scope of the invention as defined by the appended claims which follow. 

1. A plunger for an artificial lift system, the plunger comprising: a body adapted to travel within a production string positioned in a wellbore; and at least one sealing ring having an inner surface, an outer surface, a width and a thickness, the sealing ring connected about the body, wherein the width is sufficient such that when the body is disposed in the production string the outer surface contacts and substantially forms a seal between the body and an inner wall of the production string.
 2. The plunger of claim 1, wherein the production string is a tubing string.
 3. The plunger of claim 1, wherein the at least one sealing ring has a width to thickness ratio within a range from about 0.02 to about 0.2.
 4. The plunger of claim 1, wherein an outer diameter of the at least one sealing ring is between about 3% to about 6% larger than an inner diameter of the production string within which it is adapted to travel.
 5. The plunger of claim 1, wherein an outer diameter of the at least one sealing ring is about 5% larger than an inner diameter of the production string within which the body is adapted to travel.
 6. The plunger of claim 1, wherein the at least one sealing ring comprises: an inner portion proximate the inner surface formed of a substantially rigid material; and an outer portion extending from the inner portion to the outer surface formed of a material substantially flexible relative to the inner portion.
 7. The plunger of claim 1, wherein the body forms a recess and wherein the at least one sealing ring is connected to the body in the recess.
 8. The plunger of claim 1, wherein the at least one sealing ring comprises: at least one sealing ring connected about the body proximate a top end of the body; and at least one sealing ring connected about the body proximate a bottom end of the body.
 9. The plunger of claim 1, wherein when the body is disposed within the production string the at least one sealing ring assumes a shape such that the sealing ring enhances movement of the body over the drag from the sealing contact.
 10. The plunger of claim 1, wherein the at least one sealing ring has an outside diameter greater than an inner diameter of the production tubing such that when the body is disposed within the production string an interference fit causes the sealing ring to roll-form into a constricted shape and diameter that exerts the sealing contact with the inner wall of the production string.
 11. A plunger for an artificial lift system, the plunger comprising: a solid body adapted to travel within a production string positioned in a wellbore; at least one sealing ring having an inner surface, an outer surface, a width and a thickness, the sealing ring connected about the body, wherein the width is sufficient such that when the body is disposed in the production string the outer surface contacts and substantially forms a seal between the body and an inner wall of the production string; and the at least one sealing ring having a width to thickness ratio within a range from about 0.02 to 0.2 wherein when the body is disposed within the production string the sealing ring assumes a shape such that the sealing ring enhances movement of the body over the drag from the sealing contact.
 12. The plunger of claim 11, wherein the outer diameter of the at least one sealing ring is between about 3% to about 6% larger than the inner diameter of the production string within which it is adapted to travel.
 13. The plunger of claim 11, wherein the at least one sealing ring comprises: at least one sealing ring connected about the body proximate a top end of the body; and at least one sealing ring connected about the body proximate a bottom end of the body.
 14. The plunger of claim 11, wherein the at least one sealing ring comprises: an inner portion proximate the inner surface formed of a substantially rigid material; and an outer portion extending from the inner portion to the outer surface formed of a material substantially flexible relative to the inner portion.
 15. The plunger of claim 11, wherein the at least one sealing ring comprises: an inner portion proximate the inner surface formed of a substantially rigid material; an outer portion extending from the inner portion to the outer surface formed of a material substantially flexible relative to the inner portion; at least one of the at least one sealing rings being connected about the body within a recess formed proximate a top end of the body; at least one of the at least one sealing rings being connected about the body within a recess formed proximate a bottom end of the body: and the sealing rings having an outside diameter greater than an inner diameter of the production tubing within which the body is adapted to travel such that when the body is disposed within the production string an interference fit causes the sealing rings to roll-form into a constricted shape and diameter that exerts the sealing contact with the production string.
 16. A plunger for an artificial lift system, the plunger comprising: a solid body adapted to travel within a production string positioned in a wellbore; at least one sealing ring having an inner surface, an outer surface, a width and a thickness, the sealing ring connected about the body, wherein the width is sufficient such that when the body is disposed in the production string the outer surface contacts and substantially forms a seal between the body and an inner wall of the production string; and the at least one sealing ring having an outer diameter that is between about 3% to about 6% larger than an inner diameter of the production string within which it is adapted to travel.
 17. The plunger of claim 16, wherein the at least one sealing ring has a width to thickness ratio within a range from about 0.02 to about 0.2.
 18. The plunger of claim 16, wherein the at least one sealing ring comprises: an inner portion proximate the inner surface formed of a substantially rigid material; and an outer portion extending from the inner portion to the outer surface formed of a material substantially flexible relative to the inner portion.
 19. The plunger of claim 16, wherein the at least one sealing ring comprises: at least one of the at least one sealing rings being connected about the body within a recess formed proximate a top end of the body; and at least one of the at least one sealing rings being connected about the body within a recess formed proximate a bottom end of the body.
 20. The plunger of claim 16, wherein the at least one sealing ring comprises: an inner portion proximate the inner surface formed of a substantially rigid material; an outer portion extending from the inner portion to the outer surface formed of a material substantially flexible relative to the inner portion; at least one of the at least one sealing rings being connected about the body within a recess formed proximate a top end of the body; at least one of the at least one sealing rings being connected about the body within a recess formed proximate a bottom end of the body: and the sealing rings having an outside diameter greater than an inner diameter of the production tubing within which the body is adapted to travel such that wherein when the body is disposed within the production string the interference fit causes the sealing rings to roll-form into a constricted shape and diameter that exerts the sealing contact with the production string. 